VASM is a VIC-20 assembly language environment featuring a full-screen
editor, TASM-like error-notification and a two pass assembler. It is
key-compatible with TASM for the subset of commands it supports to
avoid brainfarts. The only requirement is that you have at least a 16k
RAM expansion. Source code included (under the GNU General Public License).
See http://hem.bredband.net/b129764/Siders/ for the Siders homepage.